/*
 * @(#)TimeInRangeFunction.java
 *
 * Copyright 2003-2005 Sun Microsystems, Inc. All Rights Reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
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 *   1. Redistribution of source code must retain the above copyright notice,
 *      this list of conditions and the following disclaimer.
 * 
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 * Neither the name of Sun Microsystems, Inc. or the names of contributors may
 * be used to endorse or promote products derived from this software without
 * specific prior written permission.
 * 
 * This software is provided "AS IS," without a warranty of any kind. ALL
 * EXPRESS OR IMPLIED CONDITIONS, REPRESENTATIONS AND WARRANTIES, INCLUDING
 * ANY IMPLIED WARRANTY OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE
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package org.wso2.balana.cond;

import org.wso2.balana.ctx.EvaluationCtx;

import org.wso2.balana.attr.AttributeValue;
import org.wso2.balana.attr.BooleanAttribute;
import org.wso2.balana.attr.TimeAttribute;

import java.util.List;

/**
 * This class implements the time-in-range function, which takes three time
 * values and returns true if the first value falls between the second and the
 * third value. This function was introduced in XACML 2.0.
 * <p>
 * Note that this function allows any time ranges less than 24 hours. In other
 * words, it is not bound by normal day boundries (midnight GMT), but by the
 * minimum time in the range. This means that ranges like 9am-5pm are supported,
 * as are ranges like 5pm-9am.
 * 
 * @since 2.0
 * @author seth proctor
 */
public class TimeInRangeFunction extends FunctionBase {

	/**
	 * The identifier for this function
	 */
	public static final String NAME = FUNCTION_NS_2 + "time-in-range";

	/**
	 * The number of milliseconds in a minute
	 */
	public static final long MILLIS_PER_MINUTE = 1000 * 60;

	/**
	 * The number of milliseconds in a day
	 */
	public static final long MILLIS_PER_DAY = MILLIS_PER_MINUTE * 60 * 24;

	/**
	 * Default constructor.
	 */
	public TimeInRangeFunction() {
		super(NAME, 0, TimeAttribute.identifier, false, 3,
				BooleanAttribute.identifier, false);
	}

	/**
	 * Evaluates the time-in-range function, which takes three
	 * <code>TimeAttribute</code> values. This function return true if the first
	 * value falls between the second and third values (ie., on or after the
	 * second time and on or before the third time). If no time zone is
	 * specified for the second and/or third time value, then the timezone from
	 * the first time value is used. This lets you say
	 * time-in-range(current-time, 9am, 5pm) and always have the evaluation
	 * happen in your current-time timezone.
	 * 
	 * @param inputs
	 *            a <code>List</code> of <code>Evaluatable</code> objects
	 *            representing the arguments passed to the function
	 * @param context
	 *            the respresentation of the request
	 * 
	 * @return an <code>EvaluationResult</code> containing true or false
	 */
	public EvaluationResult evaluate(List inputs, EvaluationCtx context) {
		AttributeValue[] argValues = new AttributeValue[inputs.size()];
		EvaluationResult result = evalArgs(inputs, context, argValues);

		// check if any errors occured while resolving the inputs
		if (result != null)
			return result;

		// get the three time values
		TimeAttribute attr = (TimeAttribute) (argValues[0]);
		long middleTime = attr.getMilliseconds();
		long minTime = resolveTime(attr, (TimeAttribute) (argValues[1]));
		long maxTime = resolveTime(attr, (TimeAttribute) (argValues[2]));

		// first off, if the min and max are the same, then this can only
		// be true is the middle is also the same value
		if (minTime == maxTime)
			return EvaluationResult.getInstance(middleTime == minTime);

		// shift the minTime to 00:00:00 so we can do a normal comparison,
		// taking care to shift in the correct direction (left if the
		// maxTime is bigger, otherwise right), and making sure that we
		// handle any wrapping values for the middle time (the maxTime will
		// never wrap around 00:00:00 GMT as long as we're dealing with
		// windows of less than 24 hours)

		// the amount we're shifting
		long shiftSpan;

		// figure out the right direction and get the shift amount
		if (minTime < maxTime)
			shiftSpan = -minTime;
		else
			shiftSpan = MILLIS_PER_DAY - minTime;

		// shift the maxTime and the middleTime
		maxTime = maxTime + shiftSpan;
		middleTime = handleWrap(middleTime + shiftSpan);

		// we're in the range if the middle is now between 0 and maxTime
		return EvaluationResult.getInstance((middleTime >= 0)
				&& (middleTime <= maxTime));
	}

	/**
	 * Private helper method that is used to resolve the correct values for min
	 * and max. If an explicit timezone is provided for either, then that value
	 * gets used. Otherwise we need to pick the timezone the middle time is
	 * using, and move the other time into that timezone.
	 */
	private long resolveTime(TimeAttribute middleTime, TimeAttribute otherTime) {
		long time = otherTime.getMilliseconds();
		int tz = otherTime.getTimeZone();

		// if there's no explicit timezone, then the otherTime needs to
		// be shifted to the middleTime's timezone
		if (tz == TimeAttribute.TZ_UNSPECIFIED) {
			// the other time didn't specify a timezone, so we use the
			// timezone specified in the middle time...
			int middleTz = middleTime.getTimeZone();

			// ...and we get the default timezone from the otherTime
			tz = otherTime.getDefaultedTimeZone();

			// if there was no specified timezone for the middleTime, use
			// the default timezone for that too
			if (middleTz == TimeAttribute.TZ_UNSPECIFIED)
				middleTz = middleTime.getDefaultedTimeZone();

			// use the timezone to offset the time value, if the two aren't
			// already in the same timezone
			if (middleTz != tz) {
				time -= ((middleTz - tz) * MILLIS_PER_MINUTE);
				time = handleWrap(time);
			}
		}

		return time;
	}

	/**
	 * Private helper method that handles when a time value wraps no more than
	 * 24 hours either above 23:59:59 or below 00:00:00.
	 */
	private long handleWrap(long time) {
		if (time < 0) {
			// if it's negative, add one day
			return time + MILLIS_PER_DAY;
		}

		if (time > MILLIS_PER_DAY) {
			// if it's more than 24 hours, subtract one day
			return time - MILLIS_PER_DAY;
		}

		return time;
	}

}
